1. Field of the Invention
The present invention relates to a noise variance estimation circuit and method, especially to a noise variance estimation circuit and method applicable to wireless communication.
2. Description of Related Art
Regarding a general wireless communication system, after a transmission signal arrives at a receiver through a channel, the receiver will execute channel estimation to eliminate channel effect so as to improve the performance. FIG. 1 illustrates a conventional channel estimation device 100. As it is shown in FIG. 1, the channel estimation device 100 derives channel information from a reception signal with a Least Square (LS) algorithm estimation circuit 110, and then reduces noise influence with a Channel Smoothing Scheme (CSS) circuit 120. In consideration of that the CSS circuit 120 needs to adjust its coefficient(s) according to noise variance, a noise variance estimation circuit 130 of the channel estimation device 100 will calculate such noise variance by subtracting the output of the LS algorithm estimation circuit 110 from the output of the CSS circuit 120, and will provide the noise variance for the CSS circuit 120 to determine the coefficient(s).
In light of the above, the coefficient(s) determined by the CSS circuit 120 is/are correlated with the noise variance from the noise variance estimation circuit 130, and the noise variance estimation circuit 130 determines the noise variance in accordance with the output of the CSS circuit 120. As a result, the noise variance and the decision of the coefficient(s) will interact. Providing the predetermined value(s) of the coefficient(s) of the CSS circuit 120 do(es) not fit the current channel environment, which implies that at first the noise variance estimation circuit 130 receives an output of the CSS circuit 120 failing to reflect true conditions of the current channel environment, the noise variance estimation circuit 130 will output noise variance carrying non-negligible bias in the beginning and the CSS circuit 120 will adjust its coefficient(s) according to the noise variance carrying such non-negligible bias. This interaction leads to serious error propagation and degrades the accuracy of channel estimation greatly.
People who are interested in the related arts may refer to the following literatures: U.S. Pat. Nos. 8,379,773; 8,787,473; US patent publication of Pub. No. 20100254496; and Vega, Leonardo Rey, Rey, Hernan, “A Rapid Introduction to Adaptive Filtering”, chapter 2 Wiener Filtering, ISBN 978-3-642-30299-2.